BIOLOGY Volume 2 - A Guide to General Biology - 2004

14. TRANSPORT IN ANIMALS

14.9. The Immune System

14.9.4. Immune Memory

The memory Cells mentioned in the previous section play a vital role when the body is reinfected with an antigen it has previously encountered. The population of memory cells is significantly larger than the initial pool of B lymphocytes from which they differentiated. Consequently, the response to a reinfection—known as the secondary Immune Response—develops much faster and is considerably stronger than the primary response triggered during the initial encounter with the antigen (Fig. 14.41). While the primary response may not mount quickly enough to suppress an infection, once an individual has contracted the disease and survived, subsequent exposures to the pathogen will no longer pose a threat thanks to this rapid secondary response. Every subsequent contact with the causative agent only serves to boost resistance against it. This principle forms The basis of both primary vaccination and booster shots (see the following section).

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Fig. 14.41. Primary and secondary immune responses to initial and subsequent doses of an antigen. The secondary response develops more rapidly and is more pronounced than the primary response. IgM and IgG are two classes of Antibodies (IMMUNOGLOBULINS) that differ in The Structure of their heavy chains. IgM mediates the primary response, whereas IgG drives the secondary response.